1. Field of the Invention
The present invention relates to electrical connectors, and, in particular, to such connectors designed to reduce crosstalk between adjacent conductors of different transmission paths.
2. Description of the Related Art
Near-end crosstalk refers to unwanted signals induced in one transmission path due to signals that are transmitted over one or more other transmission paths appearing at the end nearest to where the transmitted signals are injected. Near-end crosstalk often occurs when the wires and/or other conductors that form the various transmission paths are in close proximity to one another. Classic examples of near-end crosstalk are the signals induced during some voice transmissions that result in parties to one telephone call hearing the conversation of parties to another call. An example that would benefit from this invention is when high-speed data transmission is impaired due to coupling of unwanted signals from one path to another.
In a conventional telephony or data application, a signal is transmitted over a transmission path consisting of a pair of conductors, neither of which is grounded. To achieve a balanced signal, one voltage is applied to one of the conductors and another voltage having the same magnitude but opposite sign is applied to the other conductor. The difference between these two voltages is referred to as the differential voltage and their sum divided by two is referred to as the common mode voltage. When the two voltages are exactly equal in magnitude and opposite in sign, only a differential voltage will exist. A balanced signal is also referred to a differential signal. When such a differential signal is transmitted over one pair of conductors, two different types of crosstalk can be induced in an adjacent pair of conductors: differential crosstalk and common-mode crosstalk. Differential crosstalk refers to a differential or balanced signal that is induced in the adjacent pair, while common-mode crosstalk refers to a common-mode or an unbalanced signal that is induced in the adjacent pair.
Existing crosstalk compensation schemes for adjacent pairs of conductors in electrical connectors are designed to compensate for differential crosstalk on an idle pair induced (i.e., coupled) from an adjacent driven pair. In so doing, however, these schemes do not provide compensation for the differential-to-common-mode crosstalk between the driven pair and the idle pair.
FIG. 1 is a schematic drawing representing an example of an existing crosstalk compensation scheme designed to compensate for differential crosstalk between Pairs 2 and 3 in a four-pair modular mated plug/jack combination, such as those typically used for telephony or data applications (e.g., conforming to the T568-B wiring convention of the Telecommunications Industry Association (TIA) 568-A Standard). If, for example, Pair 3 is driven differentially, any coupled differential signal on Pair 2 is canceled out. Unfortunately, coupled common-mode signals on Pair 2 are not addressed by the compensation scheme of FIG. 1. The presence of this common-mode signal on Pair 2 degrades the crosstalk performance of the connector when it is deployed in a short link (known in the industry as short-link resonance). It also results in unacceptable levels of ingress and egress of electromagnetic interference. One way to compensate for this differential-to-common-mode coupling is to crossover both pairs of conductors, as shown in FIG. 2
FIG. 2 is a schematic drawing representing an example of a crosstalk compensation scheme designed to compensate for differential-to-common-mode coupling. While the compensation scheme of FIG. 2 effectively cancels out any coupled common-mode signals, it does not address differential-to-differential crosstalk.
What is needed is a crosstalk compensation scheme for connectors that addresses both differential-to-differential crosstalk as well as differential-to-common-mode crosstalk.